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Discussion Starter #1
I saw an e39 M5 differential on eBay advertised as non-working and very cheap so I bought it for spare parts.

Not working was right, here is what a 3.45:1 ring and pinion set looks like when it isn't set up right - It seems like the pinion bearings failed and that took out the ring and pinion. This is what you don't want to see inside of your differential.



While taking it apart I noticed this, which doesn't belong inside of an e39 M5 differential case :eek:



It turns out that someone had taken a BMW M-Variable differential and installed it when they did the 3.45:1 swap.

Here you can see the ring gear bolt hols spacers used to adapt the holes in the diff to the narrower size used with the 3.45:1



The M-variable diff is a different animal altogether compared to the old stand by that BMW used for years. Time to pop off the snap ring, ac couple of screws holding the case together and see what's inside:



Here are the parts:



Time to put it back together, starting with the bottom plate, first upside down then right side up:






Next comes the lower flange - this is why M-Variable diffs have one stub axle that is so long, to fit through this piece:



Friction plates - this is what makes the limited slip part work and what ultimately wears out, these look to be in very good shape:





Lower spyder gear:



Remainder of the spyder gears:



Outer case - if you are actually putting one of these together for real, you assemble everything inside of this case otherwise you will never get the spyder gears to fit properly, but when you do it that way the pictures aren't very helpful ;)


 

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Phew! I was beginning to worry about you Rob, with the fancy new wheels and shiny blower I thought you were going through something of a mid-life crisis. Now I see a diff in pieces I know there is nothing to worry about cherrsagai
 

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Its like a very cool 3D puzzle. Interesting to see the internals of these guys. These were the units used on E60s, E92s, and etc correct? (M variants of course)
 

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with all that damage, how many usable parts did you end up with?? (besides the housing and cover)
 

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Discussion Starter #6
Everything except for the ring and pinion are reuseable.
 

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Discussion Starter #8
so what you're saying is that you're taking this opportunity to finally do the 5.13 gear swap.

nice find!

I don't think I could handle something that was that fast :eek: plus I would need really wide tires.
 

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Phew! I was beginning to worry about you Rob, with the fancy new wheels and shiny blower I thought you were going through something of a mid-life crisis. Now I see a diff in pieces I know there is nothing to worry about cherrsagai
Wait, WHAT? New wheels? Where did I miss that thread???
 

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So "the difference in rotational speed that builds up between the two drive wheels whenever one of the drive wheels loses grip, either because it has become unloaded or hit a slippery surface, generates pressure spontaneously in an integrated shear pump. This pressure is then conveyed via a piston to a multiple-plate clutch, thereby channeling power to the wheel with better grip."

And "This self-controlled pump system is maintenance free and is filled with highly viscous silicon oil."

Any idea which part is the piston that acts on the clutches? Is the pump within the diff?
 

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Discussion Starter #12
So "the difference in rotational speed that builds up between the two drive wheels whenever one of the drive wheels loses grip, either because it has become unloaded or hit a slippery surface, generates pressure spontaneously in an integrated shear pump. This pressure is then conveyed via a piston to a multiple-plate clutch, thereby channeling power to the wheel with better grip."

And "This self-controlled pump system is maintenance free and is filled with highly viscous silicon oil."

Any idea which part is the piston that acts on the clutches? Is the pump within the diff?
That's not any of what's going on in the diff that I took apart, it is a conventional differential that is just layed out differently than the older 210mm differentials.
 

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Oh. I just googled "M-variable" and read about all that stuff. I guess yours is a different M-variable.
 

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Oh. I just googled "M-variable" and read about all that stuff. I guess yours is a different M-variable.
I was a bit confused earlier (earlier I asked if this was an E92/E60 diff, guess not). I believe (at least the internals) its from an E46 M3? This is from the training manual for E46 M3/E39 M5
 

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Discussion Starter #16
I don't know what car the differential originally came from. By the time it got to me it was in an e39 M5 case. I know it is a M-variable differential so it is a safe bet it was in an e46 M3.

It is exactly like the one in the pic, so it might have a pump as shown but I will have to break it down again to see if that makes any sense. If it works the way that is described in the picture then it bases its lock up on the total speed of the axle not the difference between axle speeds which makes it very undesirable from my perspective.
 

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It locks depending on axle speed differential but the amount of lockup is based on the total speed of the axle, if I am reading it correctly.
 

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Discussion Starter #19 (Edited)
When I get a chance I am going to press apart the part that should contain the "pump" I took a quick look at it it it should come apart and maybe we will see what is going inside of it.
 

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Discussion Starter #20 (Edited)
Here we go:


These pieces really aren't meant to come apart, but after 25 tons of persuasion they did :)

It was indeed a sort of pump and it was indeed filled with a very viscous fluid. The whole assembly moved a few thousandths which applied the necessary pressure on the clutches.

Here is the part of the "pump" that faces inwards



This is the other side of the inner side of the "pump"



Another picture of the inside of the plate



This is the clutch that rides inside of the viscous fluid and engages the splines of one of the stub axles, looks like it had some heat in it at one time



This is the other side of the clutch that rides on the outside of the "pump" housing



This is the inside portion of the outer plate of the "pump" housing The clutch has a very limited amount of rotational travel and you can see where the protrusions on the clutch ride and the holes in the clutch line up near the holes in the housing



25 tons of fun = a completely broken differential



 
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